1. Field of the Invention
The present invention relates to a tape carrier used for assemblage or packaging of integrated circuit chips based on a TAB system.
2. Description of the Related Art
A TAB system is known as one of the techniques for assemblage of integrated circuit chips cut out of a wafer. This method uses a film tape, called a tape carrier, which includes a film made of a synthetic resin such as polyimide. The film tape has a plurality of frames which are consecutively arranged in one line and each of which corresponds to one integrated circuit chip. Each frame of the film tape includes a multiplicity of leads formed into a predetermined pattern for connection of the integrated circuit chip to a printed circuit board. In the TAB system, the leads in each frame of the film tape and pads provided at a bonding or connection portion of the corresponding integrated circuit chip are bonded or connected en bloc.
The TAB system has features that a high-speed automatic face-up bonding is applicable and it is possible to test the bonding condition of each integrated circuit chip as connected to the film tape. Further, since it is possible to accommodate the integrated circuit chip into very small element by resin-molding the chip as bonded to the film tape by the TAB system with resin material such as epoxy resin containing fillers, the TAB system is widely applied to assemblage of the integrated circuit chips used for wrist watch, camera, calculator or the like.
A transfer molding method, as disclosed by Tummala et al on pages 578 to 604 in Microelectronics Packaging Handbook published by Van Nostrand Reinhold Company Ltd. 1989, is widely used as the method of resin-molding a chip. In the transfer molding method, a film tape having a chip mounted thereon is sandwiched between upper and lower die members of a transfer mold die and a heated and molten resin is press-injected into the resin-fill cavity formed between the upper and lower die members and is soldified. In the transfer molding method, if the molten resin is injected into the transfer mold die at a low speed, it is possible in mass production to maintain good quality of the products without causing deterioration in characteristics of wires, chips and so on thereof.
The transfer mold die has only one resin supply pot from which the resin is supplied. This is because if two resin supply pots are respectively provided in the upper and lower die members of the transfer mold die, resins supplied from two directions join to form a seam of resins which may remain after resin-molding. Though only one resin supply pot is thus provided, a film tape existing at an opening of the cavity in which the resin is to be filled divides the supplied resin into two parts, one part which enters the cavity of the upper die member and the other part which enters the cavity of the lower die member.
There are many copper leads on an upper surface of the film tape so as to make the upper surface irregular, whereas there is only a chip having a flat surface on the lower surface of the film tape so that the lower surface is substantially flat. Accordingly, when the resin is injected, the copper leads prevent the resin from smoothly flowing into the cavity of the upper mold die member, while the lower surface provides no substantial obstruction for smooth flow of the resin so that the resin is allowed to smoothly flow into the cavity of the lower mold die member. Therefore, when a conventional film tape is used, the flowing rate of the resin into the cavity of the upper mold die member is substantially different or imbalanced from that of the resin into the cavity of the lower mold die member, resulting in different conditions in solidification of the resin in the cavity between the upper mold die member and the lower mold die member thereby making difficult to obtain uniform resin-molding of the integrated circuit chip.
Also, the conventional film tape involves a problem that when the flowing rate of the resin into the resin fill cavity of the upper mold die member is imbalanced with that of the lower mold die member, the film tape is bent toward one of the upper and lower mold die members into which the flowing rate of the resin is smaller than the other, so that the flatness of the film tape is distorted thereby preventing good resin molding.
As disclosed in, for example, JP-A-2-188939, the conventional tape carrier includes a plurality of square frames each of which has at its central portion a square opening for defining the position of an integrated circuit chip to be bonded. Many leads in each frame are divided into four lead groups and the leads in each lead group extend substantially perpendicularly to one side of the square opening. One end of each lead is positioned inside the square opening and adjacent to the one side of the square opening and the other end thereof is bonded or connected to one of pads provided along the one side of the square frame. Each frame further has a plurality of elongated openings outside a mold area where the integrated circuit chip as bonded is resin-molded, that is, an area which corresponds to the cavity of a transfer mold die in which the resin is to be filled. The resin-molded integrated circuit chip is cut off from the tape carrier along the elongated openings and the leads extending from the sides of the resin-molded integrated circuit chip are connected to a printed circuit board in a subsequent process. In another type of the tape carrier, additional openings are formed in a space between an outer periphery of the mold area and the square opening along the respective sides of the square opening. In this type of the tape carrier, the cavities of the upper and lower die members of a transfer mold die communicate with each other through the additional openings. However, many leads in each lead group extending across the additional opening block the smooth flow of injected resin from one to the other of the cavities of the upper and lower die members.